1. Field of the Invention
The present invention relates generally to three dimensional optical circuits and, more particularly, to a three dimensional optical circuit assembly comprising an optical manifold and a method for making the same.
2. Background of the Invention
Optical fiber networks are becoming increasingly common in modern telecommunications systems, high speed routers, computer systems and other systems for managing large volumes of data. Optical fiber networks typically comprise a large number of optical fibers which are routed over relatively long distances in order to increase transmission speeds and efficiencies relative to the propagation of conventional electrical signals. There is often the need to route individual optical fibers between various connection points throughout a system creating an “optical circuit”. One of the more common optical circuits in use today is referred to as an “optical shuffle”. By way of example only, a simple optical shuffle may be carried out using eight optical fiber cables each having eight individual optical fibers enclosed therein. In what may be referred to as a “perfect shuffle”, using the fibers of our example here, fiber 1 of each of the eight cables coming in may be routed to a single first cable going out, and the second fiber of each of the eight cables coming in may be routed to a single second cable going out, and so forth. Referring now to FIG. 1, this particular optical shuffle is represented in a simplified schematic in which Cm refers to the input ribbon or cable, CmFn refers to the individual fibers Fn which originate in cable Cm, and Cm′ is the output ribbon or cable following the optical shuffle. It is to be understood, that although this particular example featured only 64 optical fibers, optical circuits often involve a far larger number of fibers which must be routed. Therefore, creating optical shuffles and other optical circuit structures by hand can be a tedious and highly error prone process. One can easily envision the nest of tangled optical fibers occurring in circuits between the input cables and the output cables.
Several solutions have been proposed for the creation of various optical circuits rather than simply trying to route fibers from input points to output points by hand through a large tangle of other fibers. One such solution is the use of semiautomatic machines which weave the individual fibers into the needed circuit arrangement. This solution often requires a significant financial investment in machines which are of little or no use in applications other than the weaving of optical fibers.
Another solution to the problem of creating optical circuits includes a number of attempts to route optical fibers on a flexible polymer substrate. By way of example only, one popular form of this construct is marketed as a Flex Foil®. One such approach to a flexible optical circuit solution is set forth and described in U.S. Pat. No. 5,204,925 issued to Bonanni et al. This reference describes a solution in which a flexible polymer substrate such as Mylar® or Kapton® may be coated with a pressure sensitive adhesive (PSA) and have optical fibers mounted thereon. After a number of optical fibers are laid on the substrate in the proper arrangement, a protective cover layer, usually of the same type of material as the substrate, can be bonded on top of the fibers. Of course, the exposed surface of this cover layer may subsequently be coated with an adhesive itself and additional layers of optical fibers and cover materials may be built up in the form of a laminate structure. However, the fiber lay-up process is quite labor intensive and, much like fiber weaving, would require highly specialized equipment to automate. Bonanni et al. further discloses the use of flexible side tabs or thinner strips of substrate material which extend laterally from the main body where the shuffle has occurred, and permit the optical fibers to be bent or rotated at, for example, a 90° angle to reorient the fibers from a horizontal position to a vertical position.
Another approach which incorporates a flexible optical circuit is set forth in U.S. Pat. No. 6,005,991 issued to Knasel. This particular reference discloses a printed circuit board (PCB) assembly that includes an interior portion upon which a flexible optical circuit is mounted. Much like the Bonanni et al. reference, Knasel arranges a plurality of optical fibers which are sandwiched between flexible sheets. These flexible sheets are commonly formed of Mylar® or the like and hold the optical fibers in place and are subsequently bonded to other flexible sheets using pressure sensitive adhesives, as known in the art. In this reference, space is conserved along the edge of a printed circuit board by attaching a multifiber connector to the respective first ends of the optical fibers and using single fiber connectors at the second ends of the optical fibers where space is more readily available, such as the less populated interior portion of the printed circuit board.
It should also be noted that both of these flexible circuit approaches are generally implemented in the form of large sheets with prerouted fiber networks or printed circuit boards with flexible optical circuit portions mounted thereon. In either case, these circuits normally have splices at both the input and output ends of the optical circuit to facilitate attachment to the input fiber cables and the output fiber cables during installation. Splices are normally required to overcome the length limitations of the tabs extending from the body of the flexible circuit. Additionally, splices may be used to attach specialized connectors to the input and output ends of the circuit for coupling to ruggedized cables. The splices at both the input and output end of the shuffle or optical circuit produce optical signal losses which when added across an entire optical network may be significant and unacceptable to the user. Furthermore, both mechanical and fusion splices commonly require considerable amounts of space because of the need to mechanically reinforce or strengthen the splice. Additionally, the flexible optical circuit approaches described here generally do not permit the use of protectively sheathed or “ruggedized” fiber optic ribbons leading all the way up to the flexible circuit, nor do they offer much protection to the optical fibers within the circuit or shuffle beyond the meager protection provided by a single layer of polymer film. Moreover, flexible optical circuit designs do not isolate and protect the individual fibers in that, at crossing points within the circuit, many of these fibers are in direct contact with each other.
Therefore, there is a need for three dimensional optical circuits which can be created without the expense of weaving machines and which can be more readily routed into a number of different shuffle arrangements. There is a need for an optical circuit arrangement which is less labor intensive than building up a multilayer laminate structure of Mylar® film, pressure sensitive adhesive and optical fiber, several strands of optical fiber at a time. There is also a need for an optical circuit which allows ruggedized ribbons of fiber optic cable to be run up to the circuit and away from the circuit and which provides a ruggedized protected environment for the optical fibers during the shuffle itself. There is a need for a three dimensional optical circuit having fewer fiber splices and reduced optical signal loss. Additionally, there is a need for a three dimensional optical circuit which fits into environments with limited surface area (x-y axes) by more efficiently stacking the shuffle to fully utilize space in a vertical direction (z-axis).